Elytra not working

I am trying to use the elytra, and following the right steps to activate it, it does not work. I play on a server that features a game that uses the elytra and it neither works there nor on singleplayer.
I am running LabyMod with Minecraft 1.12.2 with the mods: OptiFine, ToggleSneak, and Item Physics.
When I run Minecraft 1.12.2 with only OptiFine, it works just fine.

Is this a bug that Minecraft needs to resolve, or LabyMod?

Help is appreciated.